Ion beams are often used in the study of nuclear physics and are difficult to analyze because their intensity levels are low compared to environmental noise. Because of their low intensity levels, it is important to minimize the noise generated by scanners that are used in determining the profile of these beams.
Ion beam profile scanners, such as the one disclosed in U.S. Pat. No. 3,789,298, issued Jan. 29, 1974 to Herb, experience microphonic noise from sources such as the motion of the probe through the beam and pickup from line power. These noise sources have frequencies near the range of typical beam sample rates of 10-30 Hz. For this reason, microphonic noise is difficult to filter out from the desired signal.
In some prior art devices, such as the Herb patent referenced above, the detector is generally a cylinder coaxial with the ion beam and perpendicular with the axis of rotation of the probe. Using this detector construction, it was discovered that microphonic noise may be minimized by using an uncharged cylindrical detector. But, since charged particles are to be detected, using an uncharged detector places a severe limitation on the sensitivity of the detector. On balance, however, the loss in sensitivity was justified by the noise reduction of this design.